1. Field of the Invention
The present invention relates to a conveyor roll device that is positioned between a heating furnace and a bending press, for preliminarily bending a sheet of glass that has been heated by and fed from the heating furnace and which will be fed into and pressed to a bent shape by the bending press.
2. Description of the Prior Art
Bent glass sheets such as automobile window glass panels are produced by feeding a glass sheet heated by a heating furnace to a bending press having upper and lower press dies, between which the heated glass sheet is pressed to a desired bent shape. If, however, a flat glass sheet were pressed directly to a final bent shape, the bent glass sheet would tend to crack or would not be bent accurately to desired shape.
One solution to the above problem is disclosed in U.S. Pat. No. 4,749,399. According to the disclosed solution, the peripheral edge of a heated glass sheet fed from a heating furnace is supported on a separable ring mold, and after the peripheral edge of the glass sheet is preliminarily shaped by the ring mold, the glass sheet is pressed to a desired bent shape between upper and lower dies. If the glass sheet is to be bent to a relatively large curvature, only the peripheral edge of the heated glass sheet is supported by the ring mold for a relatively long period of time until the glass sheet is pressed by the upper and lower dies. Therefore, the heated glass sheet is liable to be undesirably deformed due to gravity before it is pressed to shape.
Japanese patent publication No. 55-49018 shows a succession of conveyor rolls for feeding a glass sheet from a heating furnace into a bending press. Each of the conveyor rolls comprises a curved core and a flexible sleeve rotatably fitted over the curved core. When the heated glass sheet is fed by the conveyor rolls, the glass sheet is preliminarily bent to a curved shape by the conveyor rolls. The conveyor rolls thus serve as bending rolls for preliminarily bending the glass sheet. The flexible sleeves are loosely fitted over the corresponding cores in order for the flexible sleeves to be able to rotate on the respective cores for feeding the glass sheet. Consequently, when the conveyor rolls feed the glass sheet, the flexible sleeves vibrate on rotation around the cores, straining the glass sheet to the point where some undesirable optical distortions may develop in the finally bent glass sheet. Another problem is that a different set of curved conveyor rolls must be used when glass sheets of a different curvature are to be produced.